Net Cost-Basis, and Net Proceeds, are just the sums of every time you made a "Buy" and "Sell", respectively. (Coin-to-coin trades are treated as both a "Buy" and "Sell")
It does not reflect how much USD or other FIAT currency you originally started with. The IRS knows this, and this is the required way to report these items on the Form 8949.
Example:
Say you have $500 and you do the following:
-Buy 2 BTC for $500 on 1/15/18
-Sell 2 BTC for $1000 on 1/16/18
-Buy 2 BTC again for $1000 on 1/17/18
-Sell 2 BTC for $2000 on 1/18/18
-Buy 1 BTC for $500 on 2/10/18
-Sell 1 BTC for $500 on 2/12/18
-Buy 2 ETH for $500 on 3/10/18
-Sell 2 ETH for $600 on 3/15/18
Your Net Cost-Basis, Net Proceeds, and Gains would look like this:
Net Cost-Basis = 500 + 1000 + 500 + 500= $2500
Net Proceeds = 1000 + 2000 + 500 + 600 = $4100
Net Gain = (1000 - 500) + (2000 - 1000) + (500 - 500) + (600-500) = $1600
In this scenario, you only "put in" $500; however, your Net Cost-Basis shows $2500. In this scenario there were only 4 trades.
You can see that a high trade volume would drive up the Net Cost-Basis number up very high. This is not something that is wrong with your report. It is simply how the numbers have to be reported.